The interaction between the solar wind and the terrestrial magnetosphere is a complex, multiscale process where global-scale dynamics are fundamentally regulated by microscopic kinetic physics. We present a global two-dimensional semi-implicit particle-in-cell (PIC) simulation of the Earth’s dayside magnetosphere using the FLEKS model, bridging the gap between fluid-scale magnetohydrodynamics and kinetic-scale plasma processes. The interaction of the solar wind with the terrestrial dipole is modeled with fully kinetic ions and electrons (mass ratio $m_i/m_e = 25$), capturing the self-consistent formation of the foreshock, bow shock, and magnetosheath. The system evolves from an initial MHD state to a complex kinetic equilibrium characterized by a reforming quasi-parallel shock and a granular magnetosheath. We identify a causal link between foreshock-generated ultra-low frequency (ULF) waves, which propagate downstream, and the spatial organization of the magnetosheath, where anisotropy-driven Alfvén ion cyclotron and mirror-mode waves coexist with broadband magnetic turbulence. Particle tracking reveals that while protons are energized via a combination of Fermi acceleration and shock drift acceleration in the foreshock, backstreaming electrons are predominantly leakage particles from the thermalized magnetosheath. These results demonstrate that semi-implicit PIC simulations can effectively resolve cross-scale coupling mechanisms, such as modification of global shock geometry by kinetic instabilities, providing a comprehensive view of the collisionless dayside solar wind-magnetosphere interaction.